1. Field
This invention relates to an improved process for removing suspended solids from an oil. More particularly, it relates to a process for producing a solids-reduced oil in which suspended solids in the oil are agglomerated by adding to the oil a solids-agglomerating agent comprising a mixture of acetone and 2-butanone and separating the conglomerated solids from the oil.
2. Prior Art
The need for an effective and economical method for removing suspended solids from a hydrocarbon oil is a continuing problem in the liquid hydrocarbon fuel art. This problem is especially notable in the case of synthetic liquid fuel production, for example in the production of liquid fuels as in the coal liquefaction and shale pyrolysis art. Raw-coal liquefaction extracts and shale oils and the like, usually contain appreciable amounts of finely divided suspended solids. These solids seriously interfere with the catalyzed oil processing steps normally required for satisfactory upgrading of these oils to useful fuels. The nature of the interference varies, depending upon the particular catalyst involved, including, for example, catalyst deactivation by poisoning active sites, pore plugging, reactor plugging and the like undesirable effects. Typically oil-suspendible solids have average diameters in the range below about 100 microns and are commonly described in the art as unfilterable solids because, as a practical matter, satisfactory separation thereof from the oil cannot be accomplished by usual mechanical separation techniques, including filtration, centrifugation and settling (see, for example, U.S. Pat. No. 3,997,425, Gatsis et al). A variety of treatments for oils containing suspended solids have been proposed in the art but, in general, each method suffers from some disadvantage. One group of related references discloses processes in which an oil containing finely divided suspended solids is fractionated into a hydrogen-rich fraction and hydrogen-poor fraction, usually by employing one or more selective solvents. Disadvantages of these processes include: (1) the development of multiple oil-containing process streams; (2) while the solids tend to become concentrated in a single process stream, nevertheless each stream usually contains some suspended solids; and (3) the selective solvents usually reject a portion of the raw oil, for example pitch, resins or polycyclic hydrocarbons which can constitute useful products as a result of subsequent hydrogenation and hydrocracking of the treated oil. Representative references in this group include (1) U.S. Pat. No. 3,018,241, E. Gorin; (2) U.S. Pat. No. 3,583,900, J. G. Gatsis; (3) U.S. Pat. No. 3,598,717, G. R. Funagel et al; and (4) U.S. Pat. No. 3,598,718, W. K. T. Gleim et al.
In another group of references, processes are disclosed wherein solids-contaminated oil is treated with water or an aqueous solution containing a chemical agent, for example a mineral acid. U.S. Pat. No. 3,232,861, E. Gorin et al, discloses a process for preferentially removing unfilterable solids using an aqueous solution of a mineral acid. U.S. Pat. No. 3,184,401, E. Gorin, suggests using an aqueous deashing agent. U.S. Pat. No. 4,012,314, W. M. Goldberger et al, discloses a process wherein the specific gravity of a liquid coal oil is reduced and by means of centrifugal action suspended solids in the oil are driven into the aqueous layer. Disadvantages in employing aqueous solutions include (1) a preferential treatment for the removal of only certain solids leaves undesirable residual suspended solids in the oil; (2) the separation of oil and water phases, especially where suspended finely divided solids are present, is usually beset by the formation of cuff-layers at the interface of the liquid phase; (3) acidifid aqueous solutions are unduly corrosive; (4) the resulting treated oil must usually be dried before it can be contacted with a catalyst in a subsequent catalyzed processing step; and (5) oil loss on solids is high.
Another group of references discloses processes in which an anti-solvent for a solids-precipitating agent is employed. In U.S. Pat. No. 3,010,893, M. D. Kulik, a process is disclosed for separating finely divided solids from low-temperature coal carbonization tars wherein a selective solvent added to the oil rejects (precipitates) a portion of the oil. The rejected oil acts as a binder for the solids, forming a tacky solid therewith. In U.S. Pat. No. 2,774,716, M. D. Kulik, a process is disclosed in which a solids-precipitating solvent, a recycle fraction from the process stream, is added to the oil. U.S. Pat. No. 3,535,224, R. S. Corey et al, discloses adding a chlorinated hydrocarbon to the oil as a solids-precipitating agent. U.S. Pat. No. 2,144,409, M. Pier et al, discloses a process for removing solids and hard asphalts from an oil by adding C.sub.6 -C.sub.10 hydrocarbon solvent to the oil, the latter being at a temperature near the critical temperature of the C.sub.6 -C.sub.10 hydrocarbon. U.S. Pat. No. 3,162,594, E. Gorin, discloses a process for removing solids from a non-distillable liquefied coal extract by catalytically hydrogenating the extract, thereby forming a non-destillable liquid containing less ash sized below 0.01 micron in diameter. U.S. Pat. No. 3,687,837 and U.S. Pat. No. 3,790,467, R. J. Fiocco et al, disclose partially precipitating solids or partially clarifying liquefied coal extracts by recycling a selected fraction of the clarified coal extract. The -467 patent discloses that the precipitated ash contains extractable organic constituents. U.S. Pat. No. 3,791,956, E. Gorin et al, provides a background of the solids-removal prior art and a process for removing suspended solids from a coal liquefaction oil wherein a precipitating solvent is added. U.S. Pat. No. 3,997,425, J. G. Gatsis et al, discloses a process for precipitating suspended solids from a liquefied coal oil by adding a light aromatic solvent to the oil.
A number of disadvantages are experienced in the use of ordinary solids-precipitating solvents, anti-solvents and the like, including (1) usually the precipitate is a tacky solid or semi-solid, for example an asphaltene, resinous solvent, etc., the latter functioning as a binder for agglomerated formerly suspended solids; (2) tacky solids undesirably adhere to surfaces of process equipment; (3) rejected portions of the oils represent an appreciable loss of product; (4) a precipitating agent such as a chlorinated hydrocarbon is often a source of corrosive hydrochloric acid in downstream process steps, the acid arising as a degradation product under severe processing conditions required to upgrade a raw oil; (5) chlorinated hydrocarbons under mild non-degrading conditions are undesirable persistent environmental pollutants; (6) a partial removal of suspended solids relative to an essentially complete removal is unsatisfactory.
The above-identified United States Patents are hereby referred to and are incorporated herein by reference thereto.
It is an object herein to provide a process for effectively separating unfilterable suspended solids from a non-distillable oil.
Another object is to carry out the aforesaid separation with essentially complete recovery of the oil.
A yet further object is to carry out the aforesaid separation without fractioning the oil into hyrogen-rich and hydrogen-poor fractions.